The present invention relates to semiconductor devices and electronic equipment or apparatuses using such semiconductor devices and more particularly, to a semiconductor device which operates at a very high speed and realizes a very high integration density and also to electronic equipment or apparatuses using such semiconductor devices.
Electronic equipment have been significantly advanced and remarkable progresses have been continued in recent years particularly in improving an operational speed or in achieving a higher integration. When high-speed electronic equipment is available, various sorts of processings can be realized easily and inexpensively. Further, improvement of the integration density enables realization of a sophisticated function. This tendency is remarkable, in particular, in a semiconductor device field. In this way, the improvement in the operational speed of electronic circuits, electronic equipment and semiconductor devices as well as the higher integration thereof are becoming the motive of advances and developments of the electronic industry.
A higher integration of semiconductor device increases the number of circuits to be incorporated in the device to thereby increase the number of pins of the semiconductor device necessary for connection with other devices. One of solutions to the above problem is disclosed in the specification of U.S. Pat. No. 5,216,278 which is directed to such a technique as to employ a ball grid array (BGA) package. The semiconductor device is accommodated in the BGA package to thereby form a BGA type semiconductor device.
Explanation will be made as to a prior art BGA type semiconductor device with reference to drawings.
FIG. 9 is a top view of a BGA board 1 for use in a BGA type semiconductor device. In the figure, a BGA board 1 is a wiring board which comprises a printed circuit board of organic material or ceramic. It is the semiconductor element that is mounted at a semiconductor device mounting area or position 5 in the center of the BGA board 1. Bonding pads 4 are provided on the BGA board 1 for bonding. The pads 4 and electrodes on the semiconductor element are electrically connected by bonding wires or the like. Extended substantially radially from the respective bonding pads 4 are a pattern of wires 3 which in turn are connected at their one ends with associated through holes 2. The density of the patterned wires 3 is high in the center of the BGA board 1. For the purpose of avoiding this, the through holes 2 are arranged along the outer periphery of the BGA board 1.
FIG. 10 shows a rear view of the BGA board 1. In the figure, the through holes 2 are used to interconnect the front and rear wiring lines of the BGA board 1. More in detail, on the rear side of the BGA board 1, wiring lines 6, which extend from the associated through holes 2, are connected to soldering pads 7. The pads 7 are arranged in a two-dimensional positional relation. More specifically, in the example of FIG. 10, the soldering pads in 3 rows are arranged along the four sides of the board 1 not in a single row but in a two-dimensional arrangement having a width.
FIG. 11 shows a cross-sectional view of a major part of the BGA board 1 under such a condition that a semiconductor element 8 is mounted on the BGA board 1. Electrodes on the semiconductor element 8 and the bonding pads 4 on the bonding pads 4 are connected by bonding wires 9. The wiring extends from the bonding pads 4 via the patterned wires 3, through holes 2 and Wiring lines 6 to the soldering pads 7. Connected to the soldering pads 7 are solder balls 10. Though not illustrated, the BGA type semiconductor device is mounted on a printed circuit board by means of the solder balls 10 to be electrically connected to other device.
The aforementioned BGA type semiconductor device features that this type of device can have a more increased number of pins than another package such as dual in-line package (DIP) or quad flat package (QFP), under the same outer dimensions. This feature results from the fact that the soldering pads 7 shown in FIG. 10 are arranged in the 2-dimensional form which does not exist in the other packages. For this reason, even when a higher integration of semiconductor device increases the number of circuits to be incorporated therein and also the number of pins therefor, there can be realized a semiconductor device which prevents its outer dimensions from being made large in scale, which contributes to the advances and developments of the electronic industry.
However, when a semiconductor device is further improved in its operational speed or when its integration is further enhanced, it may sometimes occur that the conventional BGA type semiconductor device cannot cope with it.
One of important factors upon using the semiconductor device is power supply noise. When the semiconductor device operates, it consumes power. Since current consumption varies depending on the operation of its internal circuits, power supply noise is caused by the impedance of wires in a power supply system. Assuming that power supply noise is denoted by xcex94V, the impedance of a power supply system is by Z, and current consumption variation is by xcex94I; then a relationship among these 3 factors is expressed by an equation xcex94V=Zxc3x97xcex94I.
In the case of the semiconductor device, the impedance of the power supply system is based on an inductance L of wires within the semiconductor device. Accordingly, assuming that the semiconductor device has an operational frequency f, then the impedance Z of the power supply system satisfies an equation Z=2xcfx80fL.
In the case of the printed circuit board having the semiconductor device mounted thereon, since the impedance of the power supply system is suppressed to a low value by a bypass capacitor, planar power supply/grounding wirings or other means; the impedance of the entire power supply system is, in many cases, based primarily on the inductance L of wires within the semiconductor device.
Therefore, as expressed by xcex94V=2xcfx80fLxc3x97xcex94I, the power supply noise xcex94V is generated by the operational frequency f, the inductance L of wires within the semiconductor device and the current consumption variation component xcex94I.
When the power supply noise becomes excessive, the semiconductor device erroneously operates. This is because a power supply voltage deviates from a normal operational range of the circuit within the semiconductor device, or the power supply noise is superimposed on signal wirings to cause erroneous operation of other circuits. For this reason, if the power noise is not suppressed to a prescribed value or less, erroneous operation occurs in the semiconductor device, thus disabling use of the device.
When the operational frequency f of the semiconductor device is increased, this causes an increase of the power supply noise in accordance with the aforementioned equation xcex94V=2xcfx80fLxc3x97xcex94I and thus the erroneous operation of the semiconductor device, which sometimes results in that the semiconductor device becomes impossible to use.
Further, when a higher integration of semiconductor device and an increase in the number of circuits to be incorporated therein result in an increase in the current consumption, this also causes an increase of the current consumption variation xcex94I. Thus, the power supply noise increases in accordance with the above equation xcex94V=2xcfx80fLxc3x97xcex94I and erroneous operation takes place in the semiconductor device, thus leading to disabled use of the semiconductor device.
Furthermore, in the case of, in particular, a CMOS semiconductor device, improvement in the operational frequency f of the semiconductor device causes the current consumption to increase in proportion to the frequency. This also results in that the power consumption variation xcex94I is increased to increase the power supply noise in accordance with the above equation xcex94V=2xcfx80fLxc3x97xcex94I, which may lead to the fact that the semiconductor device erroneously operates and becomes impossible to use.
The above will be explained in more detail in conjunction with a prior art example shown in FIGS. 9 to 11.
The linewidth of the patterned wires 3 and wiring lines 6 shown in FIGS. 9 to 11 was 0.15 mm, while the length thereof was both 5 mm. The through holes 2 had a diameter of 0.3 mm and a length (depth) of 0.8 mm. Further, the bonding wires 9 had a diameter of 0.04 mm and a length of 2 mm.
With such a structure as mentioned above, the wiring lines of the BGA board part, i.e., wiring lines including the patterned wires 3, wiring lines 6 and through holes 2 had an inductance of 5.1 nH, the bonding wire part had an inductance of 1.7 nH, and the total of the both inductances was 6.8 nH. Since the prior art BGA type semiconductor device had 5 power supply wiring lines and 5 grounding wiring lines, the total inductance Lo was 2.72 nH (=(6.8 nH/5)+(6.8 nH/5)). In this way, the wiring lines of the power supply system within the prior art BGA type semiconductor device had an inductance Lo of 2.72 nH.
The aforementioned prior art BGA type semiconductor device normally operated at the operational frequency of 110 MHz with the current consumption variation xcex94I of 0.5 A. In this case, the power noise xcex94V of the BGA type semiconductor device was 0.94 V (=2xcfx80xc3x97110 MHzxc3x972.72 nHxc3x970.5 A) and the allowable power supply noise thereof was 1 V or less. Accordingly, the aforementioned prior art BGA type semiconductor device had limits of the above conditions, i.e., the operational frequency limit of 110 MHz and the current consumption variation limit of 0.5 A.
Therefore, in such a prior art BGA type semiconductor device as shown in FIGS. 9 to 11, when the operational frequency or current consumption further increases, the power supply noise exceeds its allowable level, thus resulting in that the semiconductor device erroneously operates and becomes impossible to use.
In this way, when the operational speed of the semiconductor device is further improved or when the integration density is further increased, the prior art BGA type semiconductor device cannot correspondingly cope with it.
It is therefore an object of the present invention to provide a BGA type semiconductor device which can solve the above problem in the prior art and which can realize its higher-speed operation or higher integration density, and also to provide electronic equipment using the semiconductor device.
The above object is attained by providing a BGA type semiconductor device which can solve the above problem in the prior art. In accordance with an aspect of the present invention, there is provided a BGA type semiconductor device in which an array of wires for a power supply system within the semiconductor device is provided separately from other wires (more specifically, signal wires) to shorten the length of the wires for the power supply system, or the number of wires for the power supply system is increased, to reduce the inductance of the power supply system, thereby coping with the further improvement of the operational speed of the semiconductor device and with an additional increase in the integration density thereof.
More specifically, a semiconductor device according to the present invention is made up of a substrate, a semiconductor chip disposed on the upper surface of the substrate and a plurality of soldering pads provided on the lower surface of the substrate, wherein the substrate has a first group of through holes connected to signal wirings of the semiconductor chip and formed in an inner part from the periphery of the substrate and a second group of through holes connected to power supply wirings or grounding wirings of the semiconductor chip and disposed in a part of the substrate extending from the periphery of a semiconductor chip mounting area.
With the arrangement, it becomes possible to reduce the wiring length of the power supply system shorter than that of the signal wirings or increase the number of wirings of the power supply system, which in turn brings about the effect of reduced inductance of the power supply system.
Preferably, on the substrate upper surface are provided first bonding pads to connect signal terminals of the semiconductor chip with the signal wires and second bonding pads to connect power supply terminals or ground terminals of the semiconductor chip with the power supply wirings or returning (grounding) wires, the second bonding pads being disposed between the first bonding pads and the semiconductor chip. With the bonding pad arrangement as above, the second group of through holes for power supply or grounding can be formed without affecting wiring patterns, thereby making a high density packaging possible.
Here, the xe2x80x9cinner part from the periphery of the substratexe2x80x9d refers to an area 100 shown in FIG. 1 and the xe2x80x9cpart of the substrate extending from the periphery of a semiconductor chip mounting areaxe2x80x9d refers to an area 200 shown in FIG. 1. FIG. 1 will be described in more detail later.
Preferably, denoting the length of the one side of the substrate as a and the length of one side of the semiconductor chip as b, the inner part from the periphery of the substrate is a geographical range extending from the periphery of the substrate to (a-b)/8 and the part of the substrate extending from the periphery of a semiconductor chip mounting area is a geographical range extending from the periphery of the semiconductor chip to (a-b)/8. By forming the first and second groups of through holes within these geographical ranges, respectively, the wiring length of the power supply system can be reduced to a fourth of the length of the signal wirings, which in turn can reduce the inductance.
To summarize, in a semiconductor device according to the present invention, the array of the wires for the power supply system is arranged in the center of the BGA type semiconductor device to make the length of the wires of the power supply system shorter than that of signal wires, or the number of wires for the power supply system is increased to thereby reduce its inductance.
Further, when the BGA type semiconductor device of the present invention is applied to electronic equipment or apparatuses, the electronic equipment or apparatuses per se can operate at high speed.